Improve filter typescript def to leverage predicate functions #1155
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__tests__/List.ts
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| it('filters values based on type', () => { | ||
| class A {} | ||
| class B extends A {} | ||
| class C extends A {} |
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Please make sure to add some methods to classes B and C. Because of structural typing, TS will be fine with this case, but if you do something like:
class A {}
class B extends A {
public foo(): string {
return "B";
}
}
class C extends A {
public bar(): string {
return "C";
}
}then let l2 will have a type error.
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Thanks for pointing that out. I'll add this to the test
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Yeah you're right - this also demands a properly attributed predicate function
__tests__/List.ts
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| // arrow functions cannot define return types, we must use a normal function. | ||
| let l2: List<C> = l1.filter(function (v): v is C { | ||
| return v instanceof C; | ||
| }); |
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@astashov - this works well and isn't that awkward.
__tests__/List.ts
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| let l1 = List<A>([ new B(), new C(), new B(), new C() ]); | ||
| // Note: TypeScript requires a defined type guard to reduce the type. Since | ||
| // arrow functions cannot define return types, we must use a normal function. | ||
| let l2: List<C> = l1.filter(function (v): v is C { |
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Oh, I didn't that you can workaround that as by just using a function, nice!
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Not sure that comment is correct. Arrow functions do support return types.
Or is this about something else?
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@artursvonda oh, TIL!
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This expands the type def of filter() to return a type-limited version of the original type. Fixes #1152
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Woot! Thanks a lot for this! It was a major blocker for us during migration to 4.0.0. |
…ings * facebook/master: (146 commits) Add descriptive titles (immutable-js#1244) expect setting Record property to throw (immutable-js#1194) Change the has method of Record to be a type guard (immutable-js#1232) Add back deleteIn() and removeIn() to Record (immutable-js#1179) Fix typo: change 'hiearchy' to 'hierarchy' (immutable-js#1222) Fix typo in OrderedMap#toKeyedSeq (immutable-js#1177) Fixes missing size property in flow types. (immutable-js#1173) Fix size of count() after filtering or flattening (immutable-js#1171) Support typescript strictNullChecks (immutable-js#1168) added links to header in docs immutable-js#356 (immutable-js#1164) Replace "an Collection" with "a Collection" everywhere (immutable-js#1163) Fix syntax highlighting and wrong variable names (immutable-js#1159) 4.0.0-rc.2 Adds back delete() and clear() to Record (immutable-js#1157) Improve filter typescript def to leverage predicate functions (immutable-js#1155) Improve type for reduce() (immutable-js#1156) Significant improvments to concat type definitions. (immutable-js#1153) Update README.md (immutable-js#1150) Add note for using with webpack Readme improvement pass ...
This expands the type def of filter() to return a type-limited version of the original type.
Fixes #1152